The health effects of ozone (O3), a common outdoor air pollutant, have been shown to be attenuated in smokers. We hypothesize that hypersecretion of respiratory mucus due to smoking reduces the absorbance of O3 in the conducting airways of smokers. Due to the reduced amount of O3 absorbed in the conducting airways, the amount of O3 absorbed in the deeper respiratory airways of the lung is expected to be increased in smokers when compared to non-smokers. In previous work, we developed a bolus inhalation apparatus and measured the longitudinal distribution of O3 uptake in human lungs. Measurements were preformed in previous studies to determine flow effects and subject variability on non-smoking subjects. The objective of the present study is to determine uptake using the bolus inhalation apparatus on a population of smokers and non-smokers, allowing for a comparison between these two populations. Fractional uptake (L) is expressed as the amount of O3 absorbed during a single breath relative to the amount of O3 in the inhaled bolus. Uptake is related to the penetration volume (VP) of the bolus into the respiratory tract. In this study, the L-VP distribution will be determined from a series of 60-80 test breaths that are collected at a fixed flow of 60 L/min for each subject using the bolus apparatus. In previous studies, the human airways were modeled as a series of compartments based on fixed penetration volumes (i.e., VP < 180 ml corresponded to the conducting airways and VP > 180 ml represented the respiratory airways). To minimize the effects of differences in lung size among the individuals in this study, the anatomical dead space (VD) will be obtained by using carbon dioxide expirometry. VD is a measurement of the volume of the lung that does not take part in gas exchange, and can therefore be used as an estimate of the conducting airway volume of each subject. We will employ the mathematical solution for steady state, convection-diffusion through a straight tube for modeling the L-VP distribution. This solution relates L to an overall mass transfer coefficient (Ka) within any particular airway compartment. Values for Ka will be determined in a series of compartments proximal to the dead space volume that represent the conducting airways and another series of compartments distal to the dead space that represent the respiratory airways. The measured Ka values will then be compared between the smokers and nonsmokers. If our hypothesis is correct, then Ka values for smokers should be less than nonsmokers when VP < VD, and the opposite should be true when VP > VD.